Typically, in using motion picture film for projecting, recording, printing, scanning and like purposes, the strip film is advanced to repeatedly register an image frame or an image frame to be created at a focal positioning location of a film gate for viewing or exposing the frame at an optical axis perpendicular to the plane of the frame location or aperture and intersecting the center of the frame location. The image frame is held in focal position at the frame location by a pressure plate, pads or similar clamping system providing a window for unobstructed viewing or exposing of the image frame at the aperture.
The strip film, whether a motion picture film or otherwise, is typically formed of longitudinally successive, uniform rectangular image frames bounded between a pair of parallel rows of equidistant, uniform rectangular edge perforations of common cross sectional size, each perforation in one row being transversely aligned with a corresponding perforation in the other row.
Each image frame is typically registered with the aperture or frame location by registration pins of about the same cross sectional size and shape as the edge projections of the strip film, and that enter into and are embraced by given perforations during the aligning of the image frame with the aperture. This accelerates wear of the pins and the perforations and also causes perforation tearing. As a result, play occurs between the worn pins and perforations, and/or between the pins and torn perforations, leading to imprecise registration of the image frame with the aperture. If undersized pins were initially used to offset these problems, imprecise registration of the image frame with the aperture would exist from the start, due to play between the pins and perforations.
This problem is acute in use of high resolution electronic scanning and printing systems, which require extremely precise location of the image frame at the imaging location or film gate aperture, especially for achieving special effects. The strip film must be maintained very straight, i.e., truly flat focally, along the optical scan line in order to remain in sharp focus. For this reason, the film is typically wrapped around a portion of a cylindrical (or cylindrical arc) surface defining a curved film gate having a gate aperture. The gate supports the perforated edges of the strip film so that the image frame is advanced to and positioned over the gate aperture or imaging location. A retractable clamp holds the image frame in position during use, and is retracted for advancing the next image frame.
In typical scan line operation, the curved gate is rotated about its cylindrical axis to traverse the scan line incrementally, i.e., one line at a time, for scanning each line portion of the image frame as the gate rotates relative to the scanner, printer or other system being used. As the scan line technique requires precise positioning of the image frame at each focal line thereof (as distinguished from its focal plane) during scanning (or recording), even slightly imprecise registration of the image frame at the gate is undesirable, as it detracts from the optical quality of operation. Tolerances of total film flatness of 0.002 inch, and frame to frame registration at the gate or aperture within 0.00025 inch (one pixel), are desirable.
Various film gate arrangements are known which register film image frames with a gate aperture, for projecting, recording, printing, scanning and the like operations. Examples of such arrangements are shown in the following prior art.
U.S. Pat. No. 4,575,226 (Zahn et al.) discloses a device for photographing varying size image frames of a microfilm strip to make a uniform size copy, via a fixed size aperture of a film gate on which a frame is seated by a plate with a variable size window.
U.S. Pat. No. 1,805,948 (Lane) discloses a motion picture film printer in which superimposed negative and positive strip films move in unison past a fixed size aperture of a curved film gate for exposure. A ring mask with different size windows is disposed rotatably at the aperture to vary the exposure size.
U.S. Pat. No. 4,161,365 (Anderson et al.) discloses a film negative holder for a photographic printer, formed of hinged plates with mating apertures. One plate has fixed pins and movable pins to align a negative with the apertures and the other has mating holes for the fixed pins and oversized holes for the movable pins.
U.S. Pat. No. 2,418,943 (Jones) discloses a motion picture projector or printer for strip film with parallel rows of transversely aligned edge perforations engaged by sprockets to move the image frames to the aperture of a film gate under the constant pressure of a plate. A pair of pins move into and out of given pairs of transversely aligned perforations to register each frame at the aperture. One pin is the same size as the perforations while the other pin is undersized transversely relative to the perforations so that both pins register the frame longitudinally whereas transverse play at the undersized pin permits the same size pin to register the frame laterally. This arrangement is prone to excess pin and perforation wear and perforation tearing.
U.S. Pat. No. 4,360,254 (Nyman et al.) discloses a slide production camera for strip film with edge perforations engaged by fixed pins on a film gate to register an image frame with the gate aperture. A reciprocating pressure pad seats the frame at the aperture on the pins, and stripper fingers on the pad lift the frame from the pins for advancing the film. This arrangement is prone to excess pin and perforation wear and perforation tearing.
U.S. Pat. No. 4,522,476 (Renold) discloses a motion picture camera or projector for strip film with edge perforations engaged by reciprocating pins passing through bores in a reciprocating pressure pad to register an image frame with the aperture of a film gate. Sloped tips on the pins enter adjacent perforations during film advance so that the pins fully engage the perforations at the end of the advance to register a frame at the aperture. Lifters raise the film from the gate and the pressure pad bores strip the perforations from the pins on retracting the pads and pins. This arrangement is prone to excess pin and perforation wear and perforation tearing.
Commonly assigned U.S. Pat. No. 3,712,725 (Eckerdt) discloses a slide projector with an adapter for projecting image frames of a strip film with sprocket driven edge projections. Each frame is registered at the aperture of a film gate and then seated by a frame gate that is retracted for film advance. This arrangement does not involve excess pin and perforation wear and perforation tearing.
Commonly assigned U.S. Pat. No. 3,418,042 (Sigl) discloses a crank driven claw that engages edge perforations of a strip film to advance the film for registering its image frames with the aperture of a film gate. The film is then held flat by a frame plate for exposure. This arrangement does not involve excess pin and perforation wear and perforation tearing.
It is desirable to avoid such pin and perforation wear and perforation tearing, yet register precisely each image frame of a strip film with the aperture of a film gate, and maintain the frame in precise focal position thereat.